The present invention relates to a method and apparatus for contacting and Supporting coiled tubing during its injection into and withdrawal from a well bore. More particularly, the invention relates to drive rollers having a central driven arcuate wheel and multiple idler tires mounted on either side of the central driven wheel. The idler tires have arcuate surfaces with the same diameter as the driven wheel surface and concentric with the arcuate surface of the central driven wheel, thereby supporting the tubing over a large arc without causing severe rubbing from differential motion between the wheel assembly and the tubing.
Devices and methods for injecting coiled tubing into and retrieving it from wells are well known. Prior art coiled tubing injection systems include U.S. Pat. Nos. 6,142,406; 5,842,530; 5,839,514; 5,553,668; 5,309,990; 5,244,046; 5,234,053; 5,188,174; 5,094,340; 4,899,823; 4,673,035; 4,655,291; 4,585,061; and many other similar disclosures. In the prior art an injector at the wellhead is used to grip and control the injection and withdrawal of the tubing.
Conventional track injectors utilize gripper blocks mounted on two continuous parallel and opposed conveyor chains which are urged or pushed against the outer surface of the tubing. The interface forces between the gripper blocks and the tubing permit developing frictional forces which are used to transfer tangential loads from the conveyor chains to the tubing and vice versa. If insufficient interface force is applied to the tubing by the gripper blocks, slippage with attendant loss of control and wear occurs between the blocks and tubing. If excessive interface force is applied to the tubing by the gripper blocks, the tubing wall may be distorted and damaged or the injector may be damaged. A problem with such tracks results when the track is rotated into or out of engagement with the tubing from the sprockets at the ends of the track mounting assembly. This rotation can cause differential movement between the track and the tubing in the direction of the tubing axis so that rubbing occurs. As used in this description, the term xe2x80x9crubbingxe2x80x9d represents any of the effects induced by metal pieces moving relative to each other when in contact, such as galling, abrasion, tearing, scrubbing, or skidding. Rubbing causes undesirable wear of both the tubing and the gripper blocks.
Historically, the approach used to increase the injection forces with conventional track injectors has been to lengthen the injector while maintaining a sufficiently safe interface force between the individual gripper blocks and the tubing. U.S. Pat. No. 5,842,530 for example shows provision of substantially more gripper blocks along the length of its injector.
Other injectors utilizing two continuous, parallel, and opposing track injectors having grooved shoes or blocks mounted thereon are known in the art. These opposing track units have facing portions where the multiplicity of gripping blocks run parallel for gripping the tubing therebetween and are typically positioned in line, directly adjacent and above the wellhead.
Another approach has been to utilize a large diameter driven wheel with an annularly grooved outer diameter to conform to and support the tubing. Relatively small-diameter hold-down idler rollers radially press the tubing against the wheel to provide extra interface force between the tubing and the wheel so that high tangential frictional forces can be imparted to the tubing by the wheel without maintaining large back tensions. These hold-down rollers have arcuate faces to match the tubing, but pronounced rubbing occurs between the tubing and the roller due to differential movement at different rotational diameters of the roller face. While the mechanism of wheel type injectors is simple, inexpensive, and reliable, wheel size can be a limitation, especially for larger tubing diameters. One such wheel type injector is disclosed in U.S. Pat. No. 5,839,514.
A more recent injector system known in the art is a linear injector which pulls on only one side of the tubing. For this type of device, coiled tubing is driven along a single linear section of an endless chain conveyor with an opposing linear array of small-diameter arcuate face hold-down idler rollers. These hold-down rollers are sized to conform to the tubing, but they as a result cause the previously mentioned differential rubbing motion between the tubing and the roller face. Such a linear or one-track injector eliminates the necessity of synchronizing the two opposed sides of a conventional track type injector and is less damaging to the surface of the coiled tubing, but it requires a much longer unit, which of necessity extends much higher and requires additional overhead clearance. Additionally, such an injector is more expensive because it requires a considerable number of gripper blocks and rollers and a longer support track.
Copending U.S. Provisional Patent Application xe2x80x9cCoiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Benderxe2x80x9d, filed Jul. 11, 2001, utilizes a novel approach to imparting tangential injection forces to the tubing. That invention provides support over a larger portion of the tubing circumference by the driving means around the circumference of the tubing. By using a plurality of sets of opposed individually driven annularly grooved rollers which closely conform to the tubing and alternating the orientations of adjacent roller sets so that they are 90xc2x0 apart about the through axis of the injector, excellent tubing support is provided. That invention is light weight, compact, easy to service and changeout for different tubing sizes, low cost, and efficient. However, the small-diameter arcuate rollers of this device exhibit the same undesirable rubbing action between the roller face and the tubing as the previously mentioned injectors.
A major problem with tubing injectors of all types is differential movement between the tubing and the portion of the injector mechanism which contacts the tubing. For instance, for opposed track type machines, when the drive chain carrying the gripper blocks has a link coming off of or entering onto the sprockets of the track drive, differential motion relative to the axis of the tubing occurs as a result of the difference in rotational radii for the surface of the support groove of the rotating gripper block. This differential motion results in an axial direction rubbing of the tubing surface which results in wear of both the contact block and the tubing. While this situation also exists for the large drive wheel of wheel type injectors, rubbing due to the small difference in circumferential speed at the different radii of the tubing support blocks is small enough to not be important for the wheel. This, however, is not the case for any small-diameter hold-down rollers used with either wheel-type injectors or linear injectors. Similarly, for the simple small-diameter arcuate drive rollers used in the copending U.S. Patent Application for xe2x80x9cCoiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Bender,xe2x80x9d rubbing becomes more significant when the supporting arc of the drive roller is increased to provide more tubing support.
Elimination or minimization of the rubbing between the drive and hold-down rollers and the tubing in tubing injectors utilizing small diameter wheels is desirable for reducing both wheel and tubing wear. Minimizing such rubbing is particularly difficult when it is desirable to provide support for the tubing over a large arcuate surface in order to minimize tubing ovaling under the action of lateral loads. A significant need exists for improvements which will permit simultaneously minimizing the erosive action of rubbing and maximizing tubing support.
The present invention utilizes a novel means and method for improving the injecting of coiled tubing into and from a well by reducing the rubbing action of arcuate wheels or rollers used to guide and react against the tubing. Several embodiments are multi-tired idler rollers applicable to most types of injectors. The third embodiment is a multi-tired driven roller which is also applicable to most types of injectors, but is particularly useful in conjunction with the linear mechanical injector described in copending U.S. Provisional Patent Application xe2x80x9cCoiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Benderxe2x80x9d that is hereby incorporated by reference herein.
The embodiments of the present invention provide improved circumferential support to the tubing which they contact by supporting the tubing over a substantially longer arcuate surface than is used for other types of arcuate rollers. This increase of circumferential support thereby helps to minimize permanent ovaling of the tubing under the action of lateral forces. The deleterious differential rubbing in the tubing axial direction between the roller and the tubing which would normally result from using a longer wheel arc is minimized by segmenting the arc of the wheel into multiple independently rotating elements. By minimizing the difference between the maximum and minimum rotational diameters contacting the tubing of a wheel element, the differential movement of the contacting arcuate surfaces of the rotating element is minimized. This method and apparatus for providing additional support for the tubing by using roller assemblies consisting of multiple independent coaxial rollers having concentric arcuate contact surfaces of the same diameter markedly reduces the tubing and roller or wheel rubbing which normally occurs with grooved rollers having small diameters relative to the tubing.
When the rollers of the present invention are utilized to develop traction on the tubing in the linear mechanical injector described in copending U.S. Provisional patent application xe2x80x9cCoiled Tubing Injector Utilizing Opposed Drive Modules and Having an Integral Bender,xe2x80x9d the traction unit of that injector relies upon an array of multiple opposed pairs of annularly arcuately grooved driven roller assemblies which are urged into contact with the tubing. The pairs of roller assemblies are mounted in an alternating pattern 90xc2x0 apart so that the tubing is well supported and urged into roundness. The arcuate surfaces of the driven roller assemblies are sized to closely conform to the nominal circular cross-section of the tubing. The driven roller assemblies consist of the drive rollers and coaxial mirror-image idler rollers on each side of the tubing contact portion of the drive roller. The arcuate surfaces of each of the drive rollers and their associated idler rollers have concentric arcs of the same diameter.
One aspect of the present invention is a roller assembly for supporting and applying transverse loads to tubing during its injection into and withdrawal from a wellbore. This roller assembly comprises: a central roller having a primary circumferential groove with a circularly arcuate cross-section; a first outer roller having a secondary circumferential groove with a circularly arcuate cross-section on an inner side of the external diameter of the first outer roller where the grooved surface is adjacent a first side of the central roller; and a second outer roller having a tertiary circumferential groove with a circularly arcuate cross-section on an inner side of the external diameter of the second outer roller where the grooved surface is adjacent a first side of the central roller; wherein the central roller and the first and second outer rollers are independently rotatable coaxial rollers, the primary, secondary and tertiary grooved surfaces having the same arc diameter and being mutually concentric to form a substantially continuous circularly arcuate tubing contact surface. The circularly arcuate tubing contact surface of the roller assembly comprises a primary groove surface that extends about 60xc2x0 and a secondary and tertiary surfaces that extent on each side of the primary groove from about 30xc2x0 to 40xc2x0.
Another aspect of the invention is an apparatus for supporting and applying transverse loads to coiled tubing during its injection into and withdrawal from a wellbore. The apparatus comprises: a central roller having a first and second mirror-image cylindrical outer rollers, the first and second outer rollers having respectively a secondary and tertiary circumferential groove with a circularly arcuate cross-section on a internal side of an outer diameter of said first and second outer rollers, one outer roller situated on each side of the central roller with the internal side facing the central roller and having a small clearance gap between the central roller and the outside rollers; wherein the central roller and the outer rollers are independently rotatable coaxial rollers, the primary, secondary and tertiary grooves having substantially equal arc diameters and being mutually concentric to form a substantially continuous circularly arcuate tubing contact surface; whereby when coiled tubing is placed in the circularly arcuate tubing contact surface, the movement of the coiled tubing will independently rotate the central and outer rollers. The apparatus may comprise a central non-rotating shaft passing through a through-bore in the central roller and the outer rollers, wherein the independently rotatable central roller and outer rollers are supported by the shaft and rotate about said shaft; or the apparatus may comprise a central rotating shaft passing through a through-bore in the central roller and the outer rollers, wherein the central roller is integral with the rotatable shaft and rotates with the rotatable shaft and the outer rollers are independently rotatable about the rotatable shaft.
Yet another aspect of the invention is a method for supporting and applying transverse and longitudinal loads to coiled tubing during its injection into and withdrawal from a wellbore. This method comprises the following steps: (a) feeding a coiled tubing through a functional path of a coiled tubing injector such that the coiled tubing is in contact with a plurality of roller assemblies. Each roller assembly having a central roller having a primary circumferential groove with a circularly arcuate cross-section, a first outer roller having an exposed secondary circumferential groove with a circularly arcuate cross-section on an inner side of said first outer roller where the secondary groove is adjacent a first side of the central roller; and a second outer roller having an exposed tertiary circumferential groove with a circularly arcuate cross-section on an inner side of the second outer roller where the tertiary groove is adjacent a second side of the central roller; wherein the central roller and the first and second outer rollers are independently rotatable coaxial rollers, the primary, secondary and tertiary grooves having the same arc diameter and being mutually concentric to form a substantially continuous circularly arcuate tubing contact surface; and (b) operating the coiled tubing injector to cause the roller assemblies to bear transversely on the coiled tubing so that tangential friction is developed between said rollers and the tubing, thereby permitting longitudinal driving forces to be transferred from the rollers to the tubing when the central rollers of the roller assemblies are rotationally driven; whereby when the coiled tubing moves by the circularly arcuate tubing contact surface the tangential friction between the rollers and the tubing cause the rollers to independently rotate.
The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.